Rover and Fluffy are unlikely to raise kids' risk of developing pet allergies, and could lower them, according to a new 18-year-long study.

The results showed that, for most of the childhood years, being exposed to a dog or cat had little effect on later allergies. However, exposure lowered the risk for some children if they were exposed to a pet during their first year of life.

Researchers studied 565 18-year-olds who had been followed from birth. They found that only during the first year of life did exposure to dogs and cats have a major effect on later sensitivity to the animal (someone who is sensitized to an animal will likely have symptoms of an allergy when exposed to it).

"We think this is a critical window," said study author Ganesa Wegienka, an epidemiologist at Henry Ford Hospital in Detroit.

Expectant mothers were recruited between 1987 and 1989 from the Detroit metro area as part of the Detroit Childhood Allergy Study, and it was their children who took part. Researchers used annual interviews to determine dog and cat exposure.

Most children with pets in the home during their first year of life had a reduced risk of allergies. Both boys and girls with a cat at home during this time had about half the risk of being sensitized to cats later on in life, and boys with a dog at home during this time had half the risk of being sensitized to dogs later on.

Girls with a dog at home during their first year had an increased risk of later being sensitized.

"I thought it was a well-designed study, it was a thorough analysis," said Dr. Tolly Epstein, an assistant professor of immunology at the University of Cincinnati. "I don't think that it answers all of our questions about pet ownership, but I think they present some important findings," said Epstein, who has researched the effect of pet exposure on allergy development but was not involved with this study.

Conflicting results
A number of studies in recent years have looked at the effect of early exposure to cats and dogs on allergies. The results have been conflicting -- some have shown a benefit from having a pet, while others have shown it may make children more allergy-prone.

Epstein published a study in 2010 that found that early exposure to dogs did not seem to put children at risk for allergic reactions later on, although that was not the case with cats.

Wegienka said a major barrier to understanding the effect of pets on allergies is practicality.

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“Realistically, you cannot do a randomized control trial because it would not be ethical (or reasonable) to randomly allocate pet keeping,” she told MyHealthNewsDaily.

But, she added, it now seems that researchers should further study the first year of life.

C-Sections, pets and allergies
Another observation places that first year further under scrutiny.

The study authors noted that babies born by Caesarian section seemed to benefit more from having a pet around – they had only one-third of the risk with a dog, and only seventy percent of the risk with a cat of developing allergies to the animal. The authors said that a possible explanation for this is that traveling through the birth canal may expose infants to more bacteria, so babies who do not do this may gain more of their microbes from household exposure.

While evidence has been conflicting, there does not seem to be a strong reason to keep a pet out of the home because of allergy concerns.

"There have been multiple studies showing that dog ownership early in life may have a protective effect," Epstein said. "I think further study is needed."